In the manufacture of paper products, such as facial tissue, bath tissue, paper towels, dinner napkins, and the like, a wide variety of product properties are imparted to the final product through the use of chemical additives applied in the wet end of the tissue making process. Three of the most important attributes imparted to tissue through the use additives and processing are bulk, strength and softness. Increasing bulk allows the tissue maker to use less fiber to produce a given volume of tissue while improving the hand feel of the tissue product. Bulk increases however need to be balanced with softness and strength. Increases in bulk may result in less inter-fiber bonding, which may reduce strength to a point where the product fails in-use and is unacceptable to the user. Any increase in strength however, must also be balanced against softness, which is generally inversely related to strength.
Higher bulk can be achieved by embossing, but embossing normally requires a relatively stiff sheet in order for the sheet to retain the embossing pattern. Increasing sheet stiffness negatively impacts softness. Conventional embossing also substantially reduces the strength of the sheet and may lower the strength below acceptable levels in an effort to attain suitable bulk. In terms of manufacturing economy, embossing adds a unit operation and decreases efficiency.
Another means of balancing bulk, softness and strength is to use a chemical debonding agent such as a quaternary ammonium compound containing long chain alkyl groups. The cationic quaternary ammonium entity allows for the material to be retained on the cellulose via ionic bonding to anionic groups on the cellulose fibers. The long chain alkyl groups provide softness to the tissue sheet by disrupting fiber-to-fiber hydrogen bonds in the sheet. The use of such debonding agents is broadly taught in the art. Such disruption of fiber-to-fiber bonds provides a two-fold purpose in increasing the softness of the tissue. First, the reduction in hydrogen bonding produces a reduction in tensile strength thereby reducing the stiffness of the sheet. Secondly, the debonded fibers provide a surface nap to the tissue web enhancing the “fuzziness” of the tissue sheet. This sheet fuzziness may also be created through use of creping as well, where sufficient interfiber bonds are broken at the outer tissue surface to provide a plethora of free fiber ends on the tissue surface. Both debonding and creping increase levels of lint and Slough in the product. Indeed, while softness increases, it is at the expense of an increase in lint and Slough in the tissue relative to an untreated control. It can also be shown that in a blended (non-layered) sheet the level of lint and Slough is inversely proportional to the tensile strength of the sheet. Lint and Slough can generally be defined as the tendency of the fibers in the paper web to be rubbed from the web when handled.
Other attempts to balance bulk, strength and softness have involved reacting wood pulp fibers with cellulose reactive agents, such as triazines, to alter the degree of hydrogen bonding between fibers. While this perhaps helps to give a product improved bulk and an improved surface feel at a given tensile strength, such products generally have poor tensile strength as a result of the reduced fiber-fiber bonding and exhibit higher Slough and lint at a given tensile strength. As such, such products generally are not satisfactory to the user.
Accordingly, there remains a need in the art for balancing bulk, strength and softness in a tissue product. Further, there is a need for a tissue product that balances these properties, while also providing a tissue product having lint and Slough levels that are acceptable to the user.